181. In a counter flow heat exchanger, hot fluid enters at 170°C & leaves at 150°C, while the cold fluid enters at 50°C & leaves at 70°C. The arithmetic mean temperature difference in this case is __________ °C. September 6, 2025 by Admin A. 20 B. 60 C. 120 D. ∞ ✅ The correct answer is option D.